Smooth, high grade recording paper which has been treated by a Super Calendar or the like is used in ink fusion transfer type thermal printers or copiers as it is known to give a clear image. This is particularly true if the recording surface has a smoothness of 100 seconds or more. By making the paper smoother so that there is better contact between the paper and the ink ribbon, more ink is transferred to the paper surface. As a result, reproduction of full tone images is improved, however reproduction of half tone images is unsatisfactory.
At present, coated paper having a high smoothness and gloss is generally not used in ink fusion transfer type thermal printers and copiers. The reason for this is that although the paper is extremely smooth so that there is uniform contact with the ink ribbon, which might be expected to give a good ink copy, transfer of ink actually takes place unevenly and image reproduction is poor.
Non-uniform transfer of ink is particularly evident in the case of smooth, high gloss art paper for printing and in the case of cast-coated paper. This is due to the fact that, as there are very few surface imperfections or cavities, molten ink does not easily stay on the paper and may be retransferred from the paper back to the ink ribbon.
Therefore, although coated paper for printing is designed to be adequate for ordinary printing applications, it is not suitable for ink fusion transfer type thermal printers and copiers.
If these problems inherent in coated printing paper could be resolved, it would be possible to use it for such printers and copiers, and images of higher quality than ever before might be obtained.
In general, in order to confer high surface smoothness on coated paper, the surface is flattened under high pressure using a Super Calendar or similar device. This paper is not as tough as high grade paper, and since it is very dense, it lacks the feeling of volume. In addition, the paper has a low gloss so that there is a very poor balance with the gloss of the image area, and a high image quality comparable to that of ordinary offset printing cannot be obtained.
The Inventors, after performing various studies aimed at resolving the aforesaid problems, found that by incorporating a minimum amount of a synthetic silica having a predetermined specific surface in the paper, good results could be achieved with coated paper manufactured by cast coating.